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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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jagged cliff, with ice dark from included rock fragments, in immediate contact with the steep mountain slope and the trees growing upon it. The trees were being uprooted and overturned by the advancing glacier (PL CHI) and their dead trunks were inclined at various angles. The trees not yet attacked were growing undisturbed, several of them beneath the very shadow of the overhanging ice cliff. The only attack upon the trees not yet reached by the ice itself was being made by the glacial stream which flowed along the ice margin. This stream had been forced westward into the forest and for some distance was flowing among the tree trunks, not having yet eroded sufficiently, or, at the base of the slope, deposited enough gravel to overturn or kill more than a very few of them.
On July 5, 1910, when the junior author revisited the western margin of Columbia Glacier, he found that the ice had not only spread and thickened since 1909 but had continued to advance southward during the ten months since his last visit. The amount of forward movement was about 840 feet and the terminus of the glacier was within 240 feet of the nearest rock ledges on the first promontory to the south, from which future measurements might conveniently be made, or from the bench mark near Station G (Map 6), still farther south.
The advance had taken the ice front over half way across the beach nearest the glacier and the marginal stream which emerged on the beach at the ice front in 1909 was gone, the water evidently escaping beneath the ice. The substantial push moraine of August, 1909, had also been destroyed by the advance and there was not as large an accumulation at the margin of the glacier. The ice was broken and splintered and upper portions were being thrust-faulted forward over the basal ice. In some cases trees were being pushed down by these upper ice splinters before the base of the ice cliff reached their roots.
Between July and September, 1910, this western margin of the glacier seemed from Heather Island to have advanced less than 120 feet. Between the latter date and June, 1911, the advance continued but as we saw the glacier only from the steamer, near the southern end of Heather Island, we cannot say how much except that it was less than 100 feet.
To summarize, the western margin of Columbia Glacier has had the following oscillations, the net advance from before 1909 to 1911 being at least 1700 feet. It is possible, in view of minor oscillations in midglacier that there were several short periods of retreat not mentioned in this table, and that the total advance was even greater.
Date of Change	Nature of Change	Amount	Observer
1892 to July 25-27, 1899	Retreat1	800 feet	Gilbert
1899 (July 25-27) to unknown date	Retreat	Not measured	
Unknown date to June 24, 1909	Advance	500 + feet2	Grant and
1909 (June 24) to Aug. 23, 1909	Advance	700 feet	Tarrand
1909 (Aug. 23) to July 5, 1910	Advance	340 feet	Martin
1910 (July 5) to Sept. 5, 1910	Advance	100-120 feet	Martin
1910 (Sept. 5) to June 21, 1911	Advance	Less than 100	Tarrand
		feet	Martin ;
> Perhaps interrupted by minor advance about 1897 or 1898. i Plus unmeasured retreat above.